class Solution {
    const int INF = 0x3f3f3f3f;
public:
    int maxProfit(vector<int>& prices) {
        int n = prices.size();
        vector<vector<int>> f(n, vector<int>(3, -INF)); // 最多两笔
        vector<vector<int>> g(n, vector<int>(3, -INF));
        f[0][0] = -prices[0];
        g[0][0] = 0;
        for(int i = 1; i < n; ++i)
        {
            for(int j = 0; j < 3; ++j)
            {
                f[i][j] = max(f[i-1][j], g[i-1][j] - prices[i]);
                g[i][j] = g[i-1][j];
                if(j-1 >= 0)
                    g[i][j] = max(g[i-1][j], f[i-1][j-1] + prices[i]);
            }
        }
        return max(g[n-1][0], max(g[n-1][1], g[n-1][2]));
    }
};